The present invention relates generally to combustion apparatuses and, more specifically, to a high frequency, pulsed fuel injector for providing a pulsed fuel supply.
Burners for combusting natural gas, fuel oil and the like are well known and are used in a wide variety of applications from home heating furnaces to aerospace. All have similar operating characteristics as well as the common goals of stable operation, low NOx emissions, low fuel consumption and long life.
Stable burner operation is critical to good operation, not only in terms of complete combustion but reduced noise and increased equipment longevity as well. It is known that burner instability is largely attributable to inadequate mixing of fuel and air prior to combustion. Too much air locally quenches the combustion reaction causing undesirable flame propagation, undesirable emission byproducts from incomplete combustion and excessive fuel usage. Conversely, too little air leads to unstable flame, incomplete products of combustion, excessive smoke, and increased noise as the flame pulsates.
Recent investigations have pointed to the desirability of providing pulsed liquid fuel injectors to enhance the atomization of a fuel jet. It is believed that modulating a fuel spray jet to encourage breakup improves combustion by forcing an early disintegration of the fuel sheet exiting the fuel injector. This has the effect of improving spray development and spray pattern.
Several configurations of pulsed combustion units have been developed to date. For example, U.S. Pat. No. 4,568,264 to Mullen et al. discloses a pulse furnace. The Mullen device includes a combustion chamber in outlet fluid communication with an elongate exhaust tube. A mixture of air and fuel is combusted in the combustion chamber, and the resultant burning gasses create a series of pressure waves. The pressure waves travel out of the combustion chamber and into the exhaust tube, creating a vacuum in the combustion chamber. The vacuum pulls a fresh quantity of air and fuel mixture into the chamber. Simultaneously, as the pressure waves in the exhaust tube reach the end of the tube, they are reflected back into the combustion chamber. The pressure waves then compress and ignite the air and fuel mixture previously drawn into the combustion starting a new combustion cycle. Reverse flow of the exhaust gasses into the air and gas supply is prevented by flapper valves. The exhaust tube is configured to create 60 to 70 pulses per second during operation. This device is marketed by Lennox Industries Inc., Dallas, Tex. under the brand name Pulse 21 Gas Furnace.
Other examples of pulsed combustion units are found, for example, in U.S. Pat. No. 4,995,376 to Hanson disclosing a device similar to Mullen""s and intended for both gas and liquid fuel. The Hanson device also utilizes an elongate exhaust tube and includes a fuel dispensing tube that must be interchanged depending on whether the fuel is gas or liquid fuel. Hanson utilizes a flapper valve to prevent reverse air flow in the intake. U.S. Pat. No. 5,428,951 to Wilson et al. discloses a flame kernel pulse actuator which incorporates an active feedback control mechanism for controlling the downstream combustion process. A pressure sensor measures acoustic oscillations within the combustion chamber. The output of the sensor is supplied to a controller for adjustment of the frequency, phase shift and amplitude of the flame kernels, thereby controlling the downstream combustion.
While these devices are somewhat effective, and in the case of the Mullen apparatus, successful commercially in the field of gas furnaces, a need for improvement exists. More specifically, a need exists for a high frequency pulsed fuel injector that would provide improved combustion efficiency, be self actuating and contain no moving parts.
Accordingly, it is a primary object of the present invention to provide a high frequency pulsed fuel injector overcoming the limitations and disadvantages of the prior art.
Another object of the present invention is to provide a high frequency pulsed fuel injector that is self contained, self actuating and contains no moving parts.
Yet another object of the present invention is to provide a high frequency pulsed fuel injector that provides a pulsed fuel jet output.
It is another object of the present invention to provide a high frequency pulsed fuel injector that facilitates high efficiency combustor operation to reduce fuel consumption and undesirable emissions.
It is yet another object of the present invention to provide a high frequency pulsed fuel injector that can be utilized for a wide variety of fuels and be implemented in a wide variety of applications.
Additional objects, advantages and other novel features of the invention will be set forth, in part, in the description that follows and will, in part, become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purposes of the present invention as described herein, a high frequency pulsed fuel injector is described. The fuel injector of the present invention incorporates a resonance tube in outlet fluid communication with a fuel nozzle.
Resonance tubes are well known in the art. In general, resonance tubes are fluidic devices that receive a pressurized fluid input and provide a pulsating fluid output. The nature of the output, such as pulse frequency and amplitude is variable and depends on the upon the dimensions of the resonance tube.
The resonance tube outlet is placed in fluid communication with a fuel nozzle. During operation of the high frequency pulsed fuel injector, fuel is directed into the nozzle and compressed air is simultaneously directed into the resonance tube. The resonance tube provides a pulsating output which is directed into the fuel nozzle. The pulsating output of the resonance tube perturbs the flow of fuel in the fuel nozzle, effectively breaking it up into discrete slugs or chunks which exit the fuel nozzle and are subsequently combusted in a combustion chamber. The combustion process is greatly enhanced by this breakup of the fuel jet directed into the combustion chamber. This is because more efficient combustion is enabled by the enhanced atomization of the fuel delivered from the high frequency pulsed fuel injector of the present invention.
According to an important aspect of the present invention, the fluid introduced into the resonance tube is compressed air, an oxidizer. This provides for a more complete mixing of the fuel with the oxidizer, enabling increased combustion efficiency.
The fuel nozzle of the present invention can be readily configured for use with many different fuels, both gas and liquid. This is done primarily by changing the geometric configuration of the internal bore and, in some cases, including a divergent nozzle placed at the output of the fuel nozzle.
Advantageously, the high frequency pulsed fuel injector of the present invention is self contained and uses no internal moving parts. This enhances longevity as well as simplifying construction. And, the high frequency pulsed fuel injector of the present invention can be retrofitted into existing burner systems by the relatively simple addition of a source of compressed air for operation of the resonance tube. In this way, significant cost savings are made possible with existing hardware by the increased efficiency of the high frequency pulsed fuel injector of the present invention.